A silicon semiconductor device having p-n-p-n junctions has been known as a device for controlling a power etc. Much attention has been paid these days to a device having p-n-p-n junctions, which is made by III-V compound semiconductor, InP/InGaAsP or GaAs/AlGaAs, etc. because the device has functions of an optical switch, optical memory and wavelength conversion so that the device can be applied to fields of an optical computer, optical switching apparatus and optic-electric integrated circuit. Such a p-n-p-n device has been described, for instance, on pages 338 to 340 of "Appld. Phys. Lett. Vol. 50 (2), 1987" by G. W. Taylor et al. The p-n-p-n device is considered to be a device comprising two transistors in which collectors and bases are jointed to each other. For this structure, the p-n-p-n device is turned on in accordance with a positive feedback effect of transistors based on electric current which is produced by a light or electric trigger when a voltage applied to the p-n-p-n device is increased. In the turning-on state of the p-n-p-n device, all of the three p-n junctions are biased in a forward direction. Under such a condition, a band structure of the p-n p-n device is the same as that of a semiconductor laser device or light emitting diode so that light is emitted from the p-n-p-n device. For the turning off of the p-n-p-n device, it has to be rapidly turned off. For this purpose, excess carriers must be expelled from the three p-n junctions which are forward-biased, or recombined therein.
A conventional circuit for driving a gated p-n-p-n device in which excess carriers are expelled from the gated p-n-p-n device has been described on pages 590 to 597 of "IEEE TRANSACTIONS ON ELECTRON DEVICES, Vol. ED-13, No. 7, July 1966". The conventional circuit for driving a gated p-n-p-n device comprises a power source for applying a predetermined polarity and level of a voltage through a serial resistance across anode and cathode electrode of the p-n-p-n device, and a gate circuit including a gate power source, a gate switch, and a gate resistance provided in series between the cathode electrode and a gate electrode of the p-n-p-n device.
In operation, when a positive voltage applied to the anode electrode of the p-n-p-n device is increased from the power source in a case where the gate switch is turned off, the p-n-p-n device is turned on. On the contrary, in a case where the gate switch is turned on at a predetermined timing when a negative voltage is applied to the anode electrode of the p-n-p-n device from the power source, holes accumulated in a p-layer to which the gate electrode is connected are expelled therefrom in accordance with an electric field induced by the gate power source. As a result, electrons accumulated in an n layer which is sandwiched between two p-layers of the p-n-p-n device are also expelled therefrom. Consequently, the gated p-n-p-n device is turned off faster than a p-n-p-n device having no gate circuit.
According to the conventional circuit for driving a gated p-n-p-n device, however, the gate circuit including the gate power source, gate switch and gate resistance must be provided therein, and the gate switch must be turned on and off at a predetermined timing. For these reasons, the construction of the circuit becomes complicated, and the cost for fabricating the circuit becomes higher.